The Struthiopteris Spicant (Blechnaceae, Polypodiopsida) Complex in Western Europe, with Proposals for Taxonomic and Nomenclatural Changes
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Author's personal copy Plant Systematics and Evolution (2019) 305:255–268 https://doi.org/10.1007/s00606-019-1565-0 ORIGINAL ARTICLE The Struthiopteris spicant (Blechnaceae, Polypodiopsida) complex in Western Europe, with proposals for taxonomic and nomenclatural changes Sonia Molino1 · Jose M. Gabriel y Galán1 · Pawel Wasowicz2 · Pablo de la Fuente1 · Emily B. Sessa3 Received: 7 August 2018 / Accepted: 9 January 2019 / Published online: 16 February 2019 © Springer-Verlag GmbH Austria, part of Springer Nature 2019 Abstract Struthiopteris spicant is a medium-sized, dimorphic fern that occurs mainly in Western Europe and Western North America. The species is quite variable, with several forms differing in frond sizes and degree of dimorphism. In addition to the typi- cal plant, in Europe two other varieties are recognized: the Iberian S. s. var. homophyllum includes plants up to 20 cm, monomorphic or subdimorphic, with fragmented cenosori; the Icelandic S. s. var. fallax comprises very small plants up to 5 cm, monomorphic, with isolated sori. Outstanding questions remain about hybridization among the different forms, their taxonomic status, and the relations between different populations. The present work aims to study additional morphological and anatomical features of the S. spicant complex in Western Europe using a statistical approach, to resolve the taxonomic position of the different forms. We observed traits ranging from the rhizome scales to the spores and used one-way ANOVA to test for significant differences between all varieties and PCA to determine whether plants assigned to different varieties can be classified statistically into distinct groups. We detected significant differences in several of the analysed traits among the varieties in the complex. Qualitative differences in pinna anatomy and epidermal cells also help segregation of the varieties considered. Our results allowed us to propose a new specific status for the Icelandic endemic var. fallax and a new endemic Spanish variety, S. s. var. pradae. Keywords Endemism · Morphology · Pteridophytes · Taxonomy Introduction Handling Editor: Ricarda Riina. Blechnaceae Newman is a subcosmopolitan family of lepto- * Jose M. Gabriel y Galán sporangiate ferns (Polypodiopsida) that includes around 250 [email protected] species (PPG1 2016). Until recently, most of this diversity Sonia Molino fell into one large genus, Blechnum L., but after evidence [email protected] accumulated concerning its non-monophyletic status (Shep- Pawel Wasowicz herd et al. 2007; Gabriel y Galán et al. 2013; Perrie et al. [email protected] 2014; Gasper et al. 2017), Blechnum was split into sev- Pablo de la Fuente eral entities (Gasper et al. 2016). In its current conception, [email protected] Blechnaceae as a whole is made up of 24 genera (PPG1 Emily B. Sessa 2016). emilysessa@ufl.edu The genus Struthiopteris Scop., as currently defined, was resurrected by Gasper et al. (2016) to accommodate small to 1 Department of Biodiversity, Ecology and Evolution, Faculty of Biology, Universidad Complutense, Avenida Jose Antonio medium size, dimorphic, pinnate species (Fig. 1). It contains Nováis, 12, 28040 Madrid, Spain five species, with a northern geographical distribution. Four 2 Icelandic Institute of Natural History, Borgir vid Nordurslod, of these species are restricted to eastern Asia, in Japan and 600 Akureyri, Iceland Taiwan: Struthiopteris niponica (Kunze) Nakai, S. hancockii 3 S. amabilis S. cas- Department of Biology, University of Florida, Box 118525, (Hance) Tagawa, (Makino) Ching, and Gainesville, FL 32611, USA tanea (Makino) Nakai (Iwatsuki 1992; Chiou et al. 1994). Vol.:(0123456789)1 3 Author's personal copy 256 S. Molino et al. Fig. 1 Forms of plants within the Struthiopteris spicant complex. a var. homophyllum (MACB 1092626); d subdimorphic: S. spicant var. Dimorphic: S. spicant var. spicant (MA 747921); b monomorphic: homophyllum (MACB 32367). Bar = 2 cm in a; 1 cm in b; 2.5 cm in S. spicant var. fallax (MACB 109359); c monomorphic: S. spicant c, d The fifth species, S. spicant (L.) Weiss, is the object of the sterile fronds have expanded pinnae without sporangia while present study. This taxon is described as a terrestrial or saxi- the fertile ones are much longer and have highly contracted colous plant, living on acid or neutral soils, with dimorphic pinnae without green tissue at maturity (Fig. 1a); b) mono- fronds: the sterile ones are lanceolate, pinnatisect, and form- morphic, in which all fronds are similar in morphology, ing a basal rosette of 20–70 cm long, and the fertile ones irrespective of the presence of sporangia (Fig. 1b, c); or c) are erect and longer, with heavily contracted pinnae which subdimorphic, in which some fronds, regardless of whether bear costal cenosori and have continuous indusia (Rolleri they bear sporangia or not, are equal or slightly longer than and Prada 2006). This species occupies a larger distribu- the rest, with slightly contracted pinnae (i.e. when fully tion than its congeners, occurring in almost all of Europe developed, they are, at least partially, narrower but with a (from Sweden, Poland, Ukraine, and Romania westwards clear area of green tissue) (Fig. 1d). to Iceland and the Iberian Peninsula), some parts of North- This variation in frond morphology in Struthiopteris spi- ern Africa (where it is rare), the Macaronesian archipela- cant has been the subject of previous research (e.g. Löve gos (Canary Islands, Madeira, and Azores Islands) and the and Löve 1966). Taxonomists have described several entities Pacific Northwest area of North America (USA: California, that have been formally recognized with different taxonomic Oregon, Washington, Alaska; Canada: British Columbia). It assignments, usually as subspecies or, more frequently, as is typically a very common element in a variety of habitats, varieties or ecological forms. In consequence, S. spicant particularly in forests (Lawalrée 1964; Nauman 1993). can be seen as a morphological complex. While most of Such a wide range has allowed a certain amount of mor- its forms have ultimately been considered to fall under the phological variation to emerge, which is mainly manifested expected variation of S. spicant s.l. and thus have been as differences in frond sizes and degree of dimorphism. neglected in local floras, some of them are widely accepted Thus, plants can be: a) dimorphic, in which there are two and regularly included in floras and taxonomic treatments. highly different types of fronds associated with function: the For example, the Pacific American plants fit the general 1 3 Author's personal copy The complex Struthiopteris spicant in Western Europe 257 dimorphic morphology of S. spicant but with larger sterile genetic variation in chloroplast, nuclear, and microsatel- fronds, up to 100 cm (Löve and Löve 1968). Variety homo- lite data between European plants from many populations phyllum (Merino) Gabriel y Galán & R. Pino (Wasowicz and between these and American populations (unpublished et al. 2017b) comprises smaller plants, with erect fronds up data). This observation coincides partially with previous to 20 cm, usually all sporogenous, monomorphic or subdi- research that also included different populations of S. spicant morphic, and with the cenosori typically fragmented and (Soltis and Soltis 1988; Korpelainen and Pietiläinen 2008). the indusia discontinuous (Merino 1898; Ormonde 1986). The scarcity of molecular differences prevents construction This variety is endemic to the northwest of the Iberian Pen- of a well supported and highly resolved phylogeny that could insula, in both Spain and Portugal (Ormonde 1986; Molino help to elucidate the taxonomy. Here, we focus primarily on et al. 2018). Finally, var. fallax (Lange) Wasowicz & Gabriel the European taxa because the variation within the North y Galán comprises very small plants, only about 2–5 cm, American group is still poorly known and the latter would usually with monomorphic fronds, uncontracted pinnae, need its own study using a comprehensive sampling. The and isolated sori. It grows exclusively in Iceland, where its present work aims to study additional morphological and scarce populations live in close proximity to (and presum- anatomical features of plants within the S. spicant complex ably are dependent on) hot springs (Wasowicz et al. 2017b). from Western Europe, in order to resolve the taxonomic The consideration of these distinct forms as varieties position of the different forms. dates back to pteridologists Lange (1880) and Christ (1904). More recently, Löve and Löve (1968) observed that: a) cul- tured plants of homophyllum and fallax maintain their traits over time, and var. homophyllum is more variable than var. Materials and methods fallax; b) both have the same chromosome number, 2n = 68, which was later corroborated by Horjales et al. (1990) for A total of 50 individuals from all the varieties of the com- var. homophyllum; and c) both are completely interfertile plex were studied (Appendix 1). Plants came either from with the typical form of S. spicant, so it is possible that herbaria or from new collections (Fig. 2). At least one hybrids may form if they come into contact. Based on voucher per sampled population has been deposited in the these ideas, Löve and Löve proposed a taxonomy in which MACB herbarium (Madrid, Biology UCM). Samples were S. spicant (sub. Blechnum spicant) was divided into two taken to represent variation in the complex throughout the subspecies: a) subsp. nipponicum (Kunze) Löve & Löve Atlantic region of Europe, including